This invention relates to electronics, and more particularly to noble metal compositions useful for producing conductor patterns adherent to substrates.
Conductor compositions which are applied to and fired on ceramic dielectric substrates usually comprise finely divided noble metal particles and inorganic binder particles, and are commonly applied to substrates using so-called "thick film" techniques, as a dispersion of inorganic powders in an inert liquid medium or vehicle. The metallic component of the composition provides the functional (conductive) utility, while the inorganic binder (e.g., glass, Bi.sub.2 O.sub.3, etc.) bonds the metal particles to one another and to the substrate. Thick film techniques are contrasted with "thin film" techniques, which involve deposition of particles by evaporation or sputtering. Thick film techniques are discussed generally in "Handbook of Materials and Processes for Electronics," C. A. Harper, Editor, McGraw-Hill, N.Y., 1970, Chapter 12.
Conductor compositions of noble metal powders and glass binders are disclosed in, e.g., Ballard et al. U.S. Pat. No. 3,450,545, which relates to compositions of noble metal, glass, and an additive from among the oxides of Rh, Ir, Ru, Cu, and Si, or silicon carbide or boron nitride. Martin U.S. Pat. No. 3,293,501 discloses the manufacture of conductive films of noble metals plus copper glasses, and discloses only glasses of high bismuth content. Buck U.S. Pat. No. 3,776,769 discloses conductor compositions, which are fired in reducing atmospheres, of noble metal, 1-50% copper or its oxide(s), and vitreous binder. The necessity of firing in an atmosphere other than air is a distinct commercial drawback.
Noble metal conductor compositions employing a glass-free binder are disclosed in White U.K. Patent No. 855,625, relating to the use of compositions of, e.g., silver plus copper oxide plus a minor proportion of a third "inert" material capable of being wetted by molten silver and copper oxide, which may be printed and fired on ceramic substrates. The inert material may be alumina, magnesia, zirconia, titania, chromic oxide, or alumina-silicate. The firing temperatures are above 940.degree.C., preferably between 1000.degree.-1100.degree.C. No inert material which melts at the firing temperature is suggested.
Glass-free gold conductor compositions having relatively high and/or narrow firing ranges are Smith U.S. Pat. Nos. 3,799,890 and 3,799,891, isued on Mar. 26, 1974, related to glass-free compositions of gold, vehicle, copper oxide, and, in U.S. Pat. No. 3,799,891, CdO. Gold/copper oxide compositions were disclosed by Gucker et al. in Am. Ceram. Soc. Bull. 46, 789 (1967).
Short U.S. Pat. No. 3,350,341 discloses silver compositions comprising a PbF.sub.2 -containing glass.
There is a distinct need in the electronics art for gold conductor compositions which use small quantities of binder than do compositions with conventional glass binders, yet achieve good adhesion to the substrate. It is desirable that the compositions achieve good adhesion at firing temperatures lower than those required by the compositions of Smith U.S. Pat. Nos. 3,799.890 and 3,799,891. Further, it is desirable that the fired conductor patterns be thermal compression bondable without the necessity of a chemical precleaning step.